The Evidence for use of a Gauntlet- Style AFO

The custom-made gauntlet-style ankle foot orthosis (AFO) is most often made by combining leather and a stiff reinforcement to create a supportive midheight orthosis. Traditionally, the reinforcement in gauntlet AFOs was made of stiff molding leather, which offered good support but was time-consuming to fabricate. Currently, thermo­plastic is most often used to give gauntlet-style AFOs their structure. The thermoplastic is enclosed in an inner and outer layer of leather, which adds padding for comfort and additional total contact support in the orthosis.

The gauntlet-style AFO is frequently used for foot and ankle pathologies that require more stability or immobilization than a foot orthosis can provide. Gauntlets are also used as an alternative to a larger rigid thermoplastic AFO. The gauntlet-style AFO has been described as the “gold standard” for ankle and midfoot pathological conditions.1 There are a variety of pathologies clinicians can address with the gauntlet-style AFO, and specific materials, trim lines, and fabrication can vary to accommodate the different needs of individual patients.

Pathologies

Figure 1. A typical gauntlet-style AFO viewed from different angles.

Gauntlet-style AFOs have been used to manage various pathol­ogies: arthritis,1,2 posterior tibial tendon dysfunction (PTTD, also called adult acquired flat foot),3-6 ankle instability, tarsal tunnel syndrome, degenerative joint disease, Charcot foot/ankle, chronic Achilles tendinitis,7 and partial foot amputation.8 PTTD and arthritis are two of the more common pathologies for which gauntlet-style AFOs are used. The leather gauntlet-style orthosis provides total contact along with accommodation, which is particularly beneficial for these foot and ankle pathologies.3

PTTD is a dysfunction of the posterior tibial tendon and often results in a triplanar deformity with the collapse of the medial longitudinal arch, hindfoot eversion, and abduction of the forefoot.9 The gauntlet-style AFO is used to reduce ambulation pain, maintain foot and ankle position, and reduce the progression of deformity over time.6,10 For management of flexible stages of PTTD, the aim is to raise the medial longitudinal arch, induce inversion, and influence adduction of the forefoot to support the posterior tibial tendon and ligamentous structures of the foot. Elftman noted that the gauntlet-style AFO provides an intimate fit for support of the foot and ankle complex and is an excellent method of stabilizing a deformity that cannot be contained using a UCBL (University of California Biomechanics Laboratory) orthosis.3 If the PTTD has progressed to cause a rigid deformity that cannot be corrected, the gauntlet-style AFO provides the benefit of total contact over the midfoot, and can reduce edge pressure that may occur with devices that have shorter orthosis trimlines (such as the UCBL). Additionally, since the gauntlet-style AFO crosses the ankle joint, more influence can comfortably be placed on the ankle complex because of the extended trimlines.

Figure 2. A fiberglass mold used for fabrication of a gauntlet-style AFO.

Recurrent and painful ankle arthritis is another pathology that can be managed conservatively with gauntlet-style AFOs. The orthotic goals of maintenance of foot and ankle position and reduction of ambulation pain are similar to PTTD management goals. Utilization of an AFO is also commonly recommended as an avenue of nonoperative management before arthrodesis is considered.2 Experts consider articular pain a significant source of arthritic ankle pain; that is, the pain is related to joint motion, particularly at the end range of motion (ROM) of the affected ankle joint.7,11 Custom gauntlet-style AFOs can be molded to minimize this end-range pain of the joints by maintaining neutral foot and ankle alignment; a neutral position of the ankle and talus provides the largest contact area to decrease articulating surface pressure.11,12 A 2009 article1 noted that although various noncustom and custom braces are available, not all are well-suited to address ankle joint arthritis specifically. “Devices like walker boot and generic ankle braces may be useful in the short term but are cumbersome, inadequate and not ideal for long-term use,”1 they wrote. Custom-made gauntlet-style AFOs offer the benefits of individual fabrication from a mold of the patient’s foot and ankle, which provides an intimate fit, and construction with durable materials (leather and thermoplastic).

Foot and ankle positioning

In many situations in which a gauntlet-style AFO is indicated, the foot and ankle complex may present with deformities. The amount of correction required to achieve a neutral position often depends on the flexibility of the foot and ankle, as well as areas of pain. Deformities that can be passively corrected to neutral positioning (such as stage I/II PTTD) can often tolerate an orthosis fabricated in neutral correction. Beitl and Noll4 wrote that casting technique is key to the successful use of these devices. They advised that practitioners take care to correct passively or manually the position of the entire foot and ankle during the casting procedure, with the ankle corrected to neutral if possible, the longitudinal arch elevated, and the forefoot brought into alignment with the tibia.4
Once a deformity becomes rigid, accommodation must be built into the orthosis to support the existing shape of the foot and ankle complex.13 In particular, the gauntlet style is suited for supporting midfoot deformities because of its circumferential design. When casting patients with arthritis and instability, Saltzman et al14 recommended that, in general, the ankle should rest in slight pronation with compensatory forefoot supination. However, they noted, complete correction of the deformities may not be possible and usually is not well tolerated by the patient.14

Gauntlet-style vs standard AFO

The typical gauntlet-style AFO design has trimlines that start proximally five inches above the ankle and end distal to the midshaft of the first metatarsal and the base of the fifth metatarsal.1 These tend to be lower-profile than standard rigid thermoplastic AFOs, and the plastic inner can be made of a thinner plastic because of the strength of its circumferential shape. Additionally, the flexibility of the design of the gauntlet-style AFO allows for some changes in volume. Some authors have reported the leather lining is “particularly helpful” when designing orthoses for patients with fragile skin or vasculitis because of its low shear.14

The objective of lower trimlines is to provide enough immobilization for support of the foot and ankle complex and reduction of pain but to allow some motion for gait. Saltzman et al14 reported that for patients with arthritis, the most popular approaches typically involve fabrication of a rigid polypropylene ankle foot orthosis. However, Saltzman et al also noted that although this method is generally well tolerated, it can cause difficulties related to excessive restriction of motion, skin irritation, or gradual fitting problems secondary to leg atrophy.14 The lower gauntlet-style design allows more flexibility, and may be considered a “semirigid” device. However, it is possible to fabricate different designs of the leather gauntlet-style orthosis that can produce different results. The plastic inner can be made of different thicknesses to increase rigidity, and trimlines of the rigid plastic can extend from the heel to the metatarsal heads or to the end of the foot. A 2006 study by Huang et al demonstrated that foot and ankle kinematics change when different designs and trimlines of plastic AFOs are used.15 Ultimately, the design details that will determine the gauntlet orthosis function (such as plastic thickness and trimline length) are decided by the clinician based on the patient’s presentation and goals for the orthosis.

Clinical studies

In a 2007 article Logue discussed the load-sharing capabilities of gauntlet-style AFOs in relation to reducing forces on the foot and ankle affected by PTTD.16 “When a semirigid device allows some dorsiflexion of the ankle, but only against resistance, the amount of resistance is presumed proportional to the amount of dorsiflexion energy absorbed by the enclosing material and thereby is prevented from acting on the attenuated foot structures,” he wrote.16 In normal gait, the tibia usually progresses forward over the ankle joint by approximately 10° of dorsiflexion followed by metatarsopha­langeal joint hyperextension after heel rise.17 These AFOs decrease the dorsiflexion moment acting on the midfoot (by allowing minimal dorsiflexion against resistance), while allowing motion at the metatarsal heads.

Logue16 suggested that for management of PTTD, ideally the dorsiflexion resistance offered by an orthosis would be enough to absorb virtually all of the dorsiflexion torque generated by the late-stance ground reaction force [GRF] while deforming only enough to allow the ankle to actually dorsiflex the amount necessary for normal step length, approximately 10°. In this way, he wrote, normal walking motion could occur with little force acting to further attenuate the connective tissue of the foot and ankle.16 Further, he suggested that optimal force absorption could possibly be estimated based on patient comfort and satisfaction in the orthosis.

In a recent study looking at gauntlet-style AFOs and PTTD,5 Neville and Houck described a case study comparing three types of AFOs with a patient with stage II PTTD. They looked at an off-the-shelf ankle brace, a solid gauntlet-style AFO, and an articulating AFO. All styles demonstrated correction in raising the medial longitudinal arch and small changes in hindfoot inversion and all had various amounts of abduction control compared to a shoe-only condition. The researchers found that, for this patient, the articulating AFO produced the greatest correction of flatfoot deformity. The authors repeated the same comparisons in a group of 15 patients with stage II PTTD and found that both custom AFOs were associated with greater hindfoot inversion and forefoot plantar flexion than a shoe-only condition, but that none of the devices provided significant correction of forefoot abduction.18

Augustin et al completed a longer-term clinical study on gauntlet-style AFOs for management of PTTD. The investigators looked at the effect of a gauntlet-style AFO for nonoperative management of 20 patients with PTTD (stages I-III).6 At an average of one-year follow up, 90% of patients had significant increases in quality of life measures and reduction of symptoms. All patients with early-stage PTTD (stage I or II) demonstrated improvement on all three of the clinical measurement tests used in the study (AOFAS [American Orthopaedic Foot and Ankle Society] hindfoot score, Foot Function Index, and short form (SF)-36 health survey). At the follow-up appointment most of the patients had continued the treatment protocol of wearing the gauntlet AFO. Two patients discontinued use because of unrelated medical problems and one stopped using the AFO secondary to symptom improvement. Almost 30% of patients in the study were affected bilaterally. The authors had information on pain medication for 15 patients: eight patients stopped using medication after bracing, three reported using lower doses of nonsteroidal anti-inflammatory drugs, and four did not use medication before or after the AFO intervention.6

Biomechanical studies

A handful of studies have investigated the biomechanics of the gauntlet-style AFO on patient and cadaver models. Raikin et al studied how effective different devices were in immobilizing a simulated prosthetic foot model by measuring resistance to movement.19 They found a gauntlet-style AFO had less resistance to plantar flexion and dorsiflexion than plaster or fiberglass casts, a standard thermoplastic AFO, and fracture boots. However, the authors stated that, in most indications for this type of orthosis, “maintenance of sagittal ankle motion is advantageous.”19

Saltzman et al looked at long-term gauntlet-style AFO users’ ROM in and out of a molded leather gauntlet-style AFO.14 They found a 70% restriction of transverse plane motion (measured by electrogoni­ometry) with use of the leather AFO compared to no brace. They also reported a significant decrease in ankle and hindfoot sagittal plane motion (measured by radiograph). Additionally, at the tibiotalar joint motion was reduced an average of 8.9°, representing a 26% reduction from the maximum amount of unbraced ankle motion. The decrease in sagittal motion at the subtalar joint was 4.4°, a 50% reduction compared to unbraced motion. The authors reported that these findings were similar to their clinical experiences, in which the gauntlet-style AFO is generally well tolerated and provides pain relief, motion restriction, and functional improvement. They also noted the gauntlet is well suited for ankle or hindfoot support in the transverse plane.

Imhauser et al studied the biomechanical effects of a selection of orthoses on the stabilization of the hindfoot and medial longitudinal arch in a cadaveric model.20 The researchers looked at a simulated flexible flat foot in their cadaveric model by sectioning key ligaments that support the medial longitudinal arch. They then tested the model with various orthotic devices, including off-the-shelf ankle braces, the UCBL, and a gauntlet-style AFO. They found that the gauntlet AFO restored the height of the midfoot but did not significantly increase calcaneal or talar dorsiflexion. The UCBL restored both arch and hindfoot kinematics, while the off-the-shelf ankle braces with no arch support did not significantly affect mid- or hindfoot kinematics. The authors suggested the gauntlet AFO’s rigid design and lack of plantar surface support (i.e., shorter distal plastic trimlines for the design tested) may explain these findings. The angle of the calcaneus was not restored by the gauntlet because the thermoplastic support only covered the heel of the patient, they noted, suggesting that a brace with more support for the plantar aspect of the foot might more effectively address kinematic changes at both the arch and hindfoot.19 This could be done in practice by extending the thermoplastic support further distally in the gauntlet-style AFO. Although UCBL devices have been shown to produce excellent hindfoot control in cadaveric models in this study and others,20,21 implementation of those corrective pressures may be difficult because of the limited surface area such devices have available, which would require high pressure concentration.16 Applying multiple simultaneous three-point pressure systems to a larger portion of the anatomy may be more comfortable and may afford better correction, Logue suggested.16 In future studies investigating both UCBL devices and different designs of gauntlet-style AFOs (i.e., trimlines and thicknesses of thermoplastic) may help deter­mine the benefits of each design.

A more recent biomechanical study referenced Imhauser et al’s work in their study design, which tested changes in stiffness of the gauntlet-style AFO with modifications for biomechanical sensor placement.22 These researchers found a decrease in the sagittal plane stiffness of the AFO after holes were drilled into the orthosis; the coronal plane was not significantly changed. They wrote that reinforcement, especially on the medial side, is needed to maintain stiffness for biomechanical testing if holes are drilled in the orthosis.22 This appears to be an important point to consider when measuring orthosis stiffness in future studies: That is, if modification holes need to be made to the AFOs for biomechanical markers, reinforcements may be needed for the orthosis to regain the same stiffness it would have if it were an intact AFO.

Conclusion

The gauntlet-style AFO has many clinical applications, and some of the most common are for PTTD and arthritis management. Additional studies on specific design parameters for gauntlet-style AFOs would help clinicians determine specific material thickness and trimlines for load-sharing and motion control.